Cell division, diversity and differentiation Flashcards
1
Q
How do eukaryotic cells reproduce
A
Duplicate their contents, split into 2 daughter cells
2
Q
How has knowledge about the cell cycle changed over time, why
A
Early researchers- could only see the behaviour of chromosomes during mitosis and cytokineses
Discovered interphase between each M phase- not much can be seen under microscopes- need sophisticated techniques to see elaborate preparations
3
Q
word for cell death
A
apoptosis
4
Q
What helps to regulate the eukaryotic cell cycle
A
checkpoints
5
Q
What are the main checkpoints in the eukaryotic cell cycle
A
G1/S (restriction point)
G2/M
Others- e.g. halfway through M, early G1
6
Q
Purpose of checkpoints
A
- Prevent uncontrolled cell division that would lead to tumours (cancer)
- To detect and repair damage to DNA (e.g. damage caused by UV light)
Because the molecular events that control the cell cycle happen in a specific sequence, they also ensure that:
- the cycle can’t be reversed
- the DNA is only replicated once during each cell cycle
7
Q
Phases of the cell cycle
A
Interphase- G1/G0, S, G2
M
8
Q
G0
A
Gap 0 phase:
- resing phase triggered in early G1 at the restriction point by a checkpoint chemical
- some cells e.g. epithelial cells lining the gut don’t have this
Events:
- cells may undergo apoptosis (programmed cell death), differentiation, or senescence
- some types of cells e.g. neurones may remain in this phase for a very long time, or indefinitely
9
Q
G1
A
Gap 1 phase- aka growth phase:
- A G1 checkpoint control mechanism ensures the cell is ready to enter S phase and begin DNA synthesis
Events:
- Cells grow and increase in size
- transcription of genes to make RNA occurs
- organelles duplicate
- Biosynthesis e.g. protein synthesis, including enzymes needed for DNA replication in S phase
- The p53 (tumour suppressor) gene helps control this phase
10
Q
S
A
synthesis phase of interphase:
- because the chromosomes are unwound and the DNA is diffuse, every module of DNA is replicated
- There is a specific sequence to the replication of genes: housekeeping genes (those which are active in all types of cells) are replicated first, genes that are normally inactive in specific types of cells are replicated last
Events:
- once the cell has entered this phase, it is committed to completing the cell cycle
- DNA replicates
- when all chromosomes have been duplicated, each one consists o a pair of identical sister chromatids
- this phase is rapid- and because the exposed DNA base pairs are more suspectable to mutagenic agents, this reduces the chances of spontaneous mutations happening
11
Q
G2
A
Gap 2 phase of interphase:
- special chemicals ensure that the cell is ready for mitosis by stimulating proteins that will be involved in making chromosomes condense and in the formation of the spindle
Events:
- cells grow
12
Q
M
A
- a checkpoint chemical triggers the condensation of chromatin
- halfway through the cycle, the metaphase checkpoint ensures that the cell is ready to complete mitosis
Events:
- cell growth stops
- nuclear division (mitosis0
- cytokinesis (cytoplasmic division)
13
Q
The importance of mitosis
A
Asexual reproduction:
- single-celled protoctists such as amoeba and paramecium divide by mitosis to produce new individuals
- some plants e.g. strawberry, reproduce asexually by forming new plants on the end of stolons (runners)
- fungi e.g. single-cell yeasts can reproduce asexually by mitosis
- asexual reproduction n is rarer in animals but some female sharks kept in captivity without any males have produced female offspring that are genetically identical to themselves
- aphids may sometimes produce eggs, by mitosis, that don’t need fertilising
Growth:
- all multicellular organisms grow by producing new cells that are genetically identical to each other and to the parent cell from which they arose by mitosis
Tissue repair:
- wounds heal when growth factors, secreted by platelets and macrophages (white blood cells) and damaged cells of the blood-vessekl walls, stimulate the proliferation of endothelial and smooth muscle cells to repair damaged blood vessels
14
Q
4 phases of mitosis
A
Prophase
Metaphase
Anaphase
Telophase
15
Q
Mitosis- prophase
A
- chromosomes that have replicated during S phase of interphase and consist of 2 identical sister chromatids now thicken and shorten as DNA supercoils
- nuclear envelope breaks down
- the centriole in animal cells (normally found within a region called a centrosome) divides and the 2 new daughter centrioles move to opposite poles of the cell
- cytoskeleton protein (tubulin) threads form a spindle between these centrioles. The spindle has a 3D structure (like lonitude lines on globe), formed from part of cytoplasm
16
Q
Mitosis- metaphase
A
- the pairs of chromatids attach to the spindle threads at the equator region
- they attach by their centromeres
17
Q
Mitosis- anaphase
A
- the centromere of each pair of chromatids splits
- motor proteins, walking along the tubulin threads, pull each sister chromatid of a pair, in opposite directions, towards opposite poles
- because the centromere goes first, the chromatids (now called chromosones) assume a V shape
18
Q
Mitosis- telophase
A
- the separated chromosomes reach teh poles
- a new nuclear envelope forms around each set of chromosomes
- the cell no contains 2 new nuclei, each genetically identical to each other and to the parent cell from which they arose
19
Q
Process by which the cell splits, describe it
A
Cytokinesis:
- in animal cells, the plasma membrane folds inwards and ‘nips in’ the cytoplasm
- in plant cells, an end plate formed where the equator of the spindle was, and new plasma membrane and cell-wall material are laid down on either side along this endolate
- 2 new daughter cells are now formed- they are genetically identical to each other and to the parent cell
20
Q
Significance of meiosis in life cycles
A
- produces genetic variation
- increases chance of survival of population when environment changes as some individuals will have characteristics that allow them to be better adapted to the change
- sexual reproduction
21
Q
What does meiosis produce, how they are used
A
- 4 haploid gametes
- when 2 gamete nuclei fuse during fertilisation, a diploid zygote is produced
- ‘meiosis’ means reduction
22
Q
Describe the starting of meiosis
A
- Occurs in diploid germ cell (primary spermatocyte/ oocyte) to produce haploid gametes
- Diploid cells undergoing meiosis are in special organs called gonads- ovaries and testes
- these cells have been in interphase before they enter meiosis
23
Q
Describe homologous chromosomes
A
- in your body cells theer are 46 chromosonrs
- 23 from mother in egg nucleus, 23 from father in sperm nucleus
- can form matching pairs- one maternal and one paternal chromosome
- containing the same alleles genes at the same places
- may have different alleles of the same genes
- similar size
24
Q
Name meiosis phases
A
- Before, during S of interphase, each chromosome is duplicated so each consist of 2 sister chromatids
- chromosomes pair up with homologous pairs
- 2 divisions- each with 4 stages
First meitotic division: - Prophase 1
- Metaphase 1
- Anaphase 1
- Telophase 1
May be brief interphase
Second meiotic division: - Prophase 2
- Metaphase 2
- Anaphase 2
- Telophase 2
Takes place in a plane at right angles to that of meiosis 1
Cytokinesis may occur at end of 2nd division
25
Q
Meiosis- P1
A
- chromatin condenses, each chromosome supercoils- can take u stains and be seen with light microscope
- nuclear envelope breaks down
- spindle threads of tubulin protein form the centriole (animal cells)
- chromosomes come together in their homologous pairs - each member of the pair consists of 2 chromatids
- crossing over non-sister chromatids wrap around each other and may swap sections so alleles are shuffled
26
Q
Crossing over diagram
A
27
Q
Meiosis- M1
A
- pairs of homologous chromosomes, still in their crossed-over state, attach along the equator of the spindle
- each attaches to spindly by its centromeere
- homologous pairs arranged randomly- members of each pair facing opposite poles of the cell- arrangement is independent assortment
- way they line up in M1 depends how they will segregate independently during A1
28
Q
Meiosis- A1
A
memebers of each pair of homologous chromosones pulled apart by motor proteins that drag them along tubulin threads of the spindle
- the centromeres don’t divide, each chromosome consists of 2 chromatids
- the crossed over areas separate from eachother- resulting in swapped areas of chromosome and allele shuffling
29
Q
Meiosis T1
A
- in most animal cells, 2 new nuclear envelopes form around each set of chromosomes, cell divides by cytokinesis
- short interphase when chromosomes uncoil
- each new nucleus contains half the original number of chromosomes, but each consists of 2 chromatids
- in most plant cells, the cell goes straight from A1 to P2
30
Q
Meiosis P2
A
- if the nuclear envelopes have reformed, they now breakdown
- the chromosomes coil and condense, each consisting of 2 chromatids
- the chromatids of each chromosome are no longer identical due to crossing over in p1
- spindles form
31
Q
Meiosis M2
A
- the chromosomes attach by their centromere to the equator of the spindle
- the chromatids of each chromosome are randomly arranged
- the way they are arranged will determine how the chromatids separate during A2
32
Q
Meiosis A2
A
- centromeres divide
- the chromatids of each chromosome are pulled apart by motor proteins that drag them along the tubulin threads of the spindle, towards opposite poles
- the chromatids are therefore randomly segregated
33
Q
meiosis T2
A
- nuclear envelopes form around each of the 4 haploid nuclei
- in animals, the 2 cells now divide to give 4 haploid cells
- in plants a tetrad of 4 haploid cells is formed
34
Q
How does meiosis produce genetic variation
A
- crossing over in P1 shuffles alleles
- independent assortment of chromosomes in A1 leads to random distribution of maternal and paternal chromosomes of each pair
- independent assortment in A2 leads to further random distribution of genetic material
- haploid gametes are produced which undergo random fusion with gametes derived from another organism of the same species
35
Q
Mitosis vs meiosis diagram
A
36
Q
Mitosis vs meiosis numbers of chromosomes/chromatids
A
42
Q
Spermatozoa adaptions
A
- many mitochondria- carry out aerobic respiration- the ATP provides energy for the undulipodium to move and propel the cell towards the ovum
- small and long- can move easily
- once the spermatozoon reaches the ovum, enzymes are released from the acrosome (a specialised lysosome)- the enzymes digest the outer protective covering of the ovum, allowing the sperm head to enter the ovum
- the head f the sperm contains the haploid male gamete nucleus and very little cytoplasm
43
Q
Where are epithelial cells found, name 2 types
A
- epithelium is lining tissue
- found on out and inside of your body
- makes up the walls of the alveloli and capillaries, and lining of intestines
- squamous epithelial cells- plattened in shape
- cillated epithelial cells- have cillia
45
Q
Palisade cells adaption
A
Adapted for photosynthesis because:
- long and cylindrical- pack together quite closely but with a little space between them for air to circulate; carbon dioxide in these air spaces diffuses into the cells
- have large vacuole so that the chloroplasts are positioned nearer to the periphery of the cell, reducing the diffusion distance for carbon dioxide
- contain many chloroplasts- carry out photosynthesis
- contain cytoskeleton threads and motor proteins to move the chloroplasts- nearer to upper surface of the leaf when sunlight intensity is low, but further down when it is high
46
Q
Guard cells location, how they work, adaptions
A
- lower epidermis- do contain chloroplasts but don’t photosynthesis as don’t have enzymes needed for 2nd stage, found in pairs
- light energy used to produce ATP
- ATP actively transports potassium ions from surrounding epidermal cells into guard cells- lowers their water potential
- water now enters the guard cells from neighbouring epidermal cells, by osmosis
- the guard cells swell, but at the tips the cellulose cell wall is more flexible, and it is more rigid where it is thicker- tips bulge, and the gap between them (stoma) enlarges
- as these stomata open, air can enter the spaces within the layer of cells beneath the palisade cells
- gaseous exchange can occur, and carbon dioxide will diffuse into the palisade cells- as they use it for photosynthesis, this maintains a steep concentration gradient
- oxygen produced during photosynthesis can diffuse out of the pallisade cells into the air spaces and out through the open stomata
- when the stomata are open, water vapour also exists from them (part of transportation)
47
Q
Where you find root hair cells, how they’re adapted
A
Epidermal cells on the outer layer of young plant roots
- hair-like projection greatly increases the surface area for absorption of water and mineral ions, such as nitrates, from the soil into which it projects
- mineral ions are actively transported into the root hair cells- lowering the water potential within them and causing water to follow by osmosis, down the water potential gradient
- have special carrier proteins in the plasma membranes in order to actively transport the mineral ions in
- these cells also produce ATP- needed for active transport
53
Q
Describe charachetristics and functios of muscle tissue
A
- well vascularised (has many blood vessels)
- mussscle cells are called fibrres- they ate elongated and contain special organelles called myofiaments made of the proteins actin and myosin- allow muscle tissue to contract
Functions:
- skeletal muscles, packaged by connective tissue sheets and joined to bones by tendons- when they contract, they cause bones to move
- cardiac muscle- makes up the walls of the heart- allows the heart to beat and pump blood
- smooth muscle- occurs in the walls of the intestine, blood vessels, uterus and urinary tracts- propels substances along these tracks
